V CADDIS-WORMS 267 



there is no firm resisting surface, and the processes 

 are not developed. Had they been true respiratory 

 organs, we may conjecture that they would have 

 been retained to supply the place of tracheal fila- 

 ments, which are altogether wanting. 



" From time to time the larva turns round in its 

 case, and even leaves it for a short space. Generally, 

 however, it remains quiet inside, apparently on the 

 alert for prey. If a Chironomus or other small 

 aquatic larva approaches, it is almost certain to get 

 entangled in the network of silken threads. At once 



o 



the Caddis in its retreat perceives the presence of a 

 possible victim. The long hairs which cover the body 

 are possibly tactile, and reveal slight disturbances of 

 the silken network. The Plectrocnemia then pro- 

 ceeds warily to determine the cause of the disturbance. 

 Should the Chironomus be entangled near the middle 

 of the tube, the Caddis-worm does not hesitate to bite 

 its way through the side, and its jaws very soon quiet 

 the struggles of the prey. 



" There is some resemblance between the snare of 

 the Plectrocnemia and the web of a Spider, but the 

 Plectrocnemia is effectually concealed by the mud 

 which clings to its retreat. In captivity it forms a 

 web which is free from foreign particles, and allows 

 all its manoeuvres to be observed." 



"The Caddis-fly," says Reaumur, "exhibits some 

 marked peculiarities of its own. In a classification 

 of Flies, we might assign to them the name of papilio- 

 naceous, that is, Flies which at first sight resemble 

 Butterflies. These papilionaceous Flies have four 

 wings, of which only the two upper are visible when 



